1. Field of the Invention
This invention relates to an interlayer having a wedged configuration to eliminate double imaging for use in an automotive windshield functioning as the combiner for a head-up display system.
2. Technical Considerations
A head-up display system is a visual display arrangement that displays information to a viewer while he simultaneously views the real world around and through the display. Head-up display systems are often incorporated into aircraft cockpits for pilots to monitor flight information. More recently the systems have been used in land vehicles such as cars, trucks and the like. The display is generally positioned so that the viewer does not have to glance downward to the vehicle dashboard and away from the viewing area in front of the vehicle as is normal for a vehicle operator in viewing the vehicle operating information.
A head-up display system generally includes a display projection system, a collimator, and a combiner. The projection system includes a light source that projects operating information through the collimator which generally aligns the projected light rays. The collimated light is then reflected off the combiner, which is in the vehicle operator""s field of view. In this manner, important vehicle information such as, for example, fuel information and vehicle speed is displayed within the operator""s field of vision through the windshield and permits the operator to safely maintain eye contact with the real world while simultaneously viewing the displayed information. The reflected images of the display may be focused anywhere from a position immediately in front of the vehicle to optical infinity.
Laminated windshields have been used as the combiner in a head-up display system to reflect a primary display image as taught in U.S. Pat. No. 2,264,044 to Lee. However, it has been observed that a secondary image is reflected off the outer surface of the windshield. This secondary image is superimposed over but offset from the primary image and reduces the overall image clarity.
It would be advantageous to have a wedged interlayer for use in a windshield for a head-up display which windshield functions as a combiner and provides a clear display image without incorporating additional components on or within the windshield.
The present invention provides a shaped interlayer blank for use with glass in a vehicle windshield. The blank is a single layer formed of plasticized polyvinyl butyral and having a quadrilateral peripheral contour with two sides of arcuate shape and a wedge-shaped thickness profile extending from the edge of one arcuate side to the edge of the other arcuate side. The interlayer is used in a windshield for a head-up display system and because of the wedge shape reduces the amount of double imaging that occurs when a laminated windshield having the wedged shaped interlayed is used as the combined in the display system.
In one particular embodiment of the invention, the windshield includes a pair of glass plies secured to each other by a sheet of thermoplastic interlayer material tapered in thickness from one edge to its opposing edge. The tapered configuration of the interlayer may be achieved by casting the interlayer to the desired configuration or differentially stretching the interlayer to the desired shape. When the glass plies and tapered interlayer are assembled and laminated to form a unitary structure, the opposing major surfaces of the laminate are non-parallel and offset at a predetermined angle such that images from a display source that are reflected off the opposing major surfaces of the laminate are substantially superimposed over each other.